Density of states in thin film transistors from the modulated photocurrent technique: application to the study of metastabilities

Abstract

We demonstrate the possibility of probing the density of states (DOS) of the active a-Si:H layer of Thin Film Transistors (TFT) by means of the modulated photocurrent technique. The DOS deduced from this technique on Top Nitride TFTs is compared with values deduced from the subthreshold slopes of the transfer characteristics. We also study the consequences of gate bias stresses on the TFTs. For gate bias stresses up to ±30V, we observe a shift in the transfer characteristics along the gate voltage axis, but did not measure any significant change in the DOS above midgap. These results are discussed and compared with those recently published in the literature by other authors.